The study will examine the metabolism of exogenous fatty acids by Macaca fascicularis. Trans fatty acids which cannot be synthesized by eukaryotes will be used as the exogenous fatty acid marker. These fatty acids are geometrical isomers of cis fatty acids which can be synthesized by eukaryotes. The trans fatty acids are catabolized and removed from the body shortly after the fatty acids are removed from the diet. Twelve male M. fascicularis monkeys are being used in the study. Six will be fed the control diet, and the others will receive the experimental diet. The objectives of the study are to determine if: (1) the monkeys have the gut flora required to produce trans fatty acids, (2) trans fatty acids are incorporated into the RBC membrane of the monkeys, and (3) the linoleate to arachidonate ratio of the erythrocyte membrane is altered.